How to find knot indexes after getting getNearestPosition

[turkerfatih]

Let's say I want to know which indexes the result point of getNearestPositionis between. As there any way?

[kjerandp]

From the response of getNearestPosition you have a value for "u". This is the uniform position along the curve (parameterized by curve length). You can use this value to get the time along the curve ("t"), using the getTimeFromPosition function. The time along the curve is directly mapped to point indices, so you can find it's lower index by multiplying it by the number of points if your curve is closed, or number of points - 1 if it's not closed:

Note that this will give you the index as a decimal number, and unless you floor the value, the fraction part will tell you how far you are from the lower bound index to the next.

Something like this:
const { u } = interp.getNearestPosition(point)
const t = interp.getTimeFromPosition(u)
const index = Math.floor(t * (interp.getPoints().length - 1)) // assumes non-closed curve

Maybe I'll add a function to the lib for this purpose if anyone finds it useful.